This invention relates in general to controls for hydraulic systems and, in particular, to a hydraulic system controller for limiting the application of hydraulic power in response to the temperature of the hydraulic fluid.
More specifically, but without restriction to the particular use which is shown and described, this invention relates to a hydraulic system controller which utilizes a temperature responsive valve to control application of hydraulic fluid power. The temperature responsive valve is actuated in response to the temperature of the hydraulic fluid utilized in the hydraulic system to thereby minimize stresses exerted on components of the system due to variations in fluid viscosity during operation.
In the use of hydraulic systems, for example as utilized in various earth moving and construction machinery equipment, the various equipment in which these hydraulic systems are employed are utilized in widely varying environmental conditions. Although many attempts have been made to develop hydraulic fluids which maintain a uniform viscosity throughout a given temperature range, these attempts have not yet produced a hydraulic fluid which does not vary in viscosity in relationship to the fluid temperature. Since the environmental conditions in which this equipment, and therefore these hydraulic systems, are employed varies throughout extreme temperatures, it has been found that in cold weather conditions the high viscosity of the hydraulic fluid creates a problem during start-up of the hydraulic system. The flow of the fluid, being very viscous, is such that the hydraulic pump is badly lubricated during start-up, and clearances between relatively movable mechanisms in the system change because of differentials in the coefficient of thermal expansion for various parts of the hydraulic pump and other components of the hydraulic system.
In order to minimize damage to the components of the hydraulic fluid system, the operator of the equipment must keep the machine engine running at a low speed until the temperature of the hydraulic fluid increases sufficiently to warm and lubricate the components of the system. However, heretofore this warm-up period has required special attention on the part of the equipment operator. The present invention eliminates the necessity of the equipment operator controlling operation of the engine by automatically limiting the pressure developed within the hydraulic fluid system in response to the temperature of the hydraulic fluid. While this invention is believed to have general application to any type of hydraulic fluid system, for convenience of illustration the preferred embodiment is described with reference to its use in earth moving or construction machinery equipment.